1. Field of the Invention
The present invention relates to a heat spreader module for cooling an IC chip used in semiconductor devices or the like, and to a method of manufacturing such a heat spreader module.
2. Description of the Related Art
Generally, a heat spreader module for effectively dissipating heat from a semiconductor device, such as an IGBT (Insulated Gate Bipolar Transistor), comprises a circuit board, an insulating board, a metal plate, and a heat spreader (heat diffusion layer). Further, a heat sink is connected to the lower surface of the heat spreader.
Heretofore, it has been widely practiced to join the components of the heat spreader module using a solder layer having a melting point of about 250° C. However, the solder layer poses a large heat transfer resistance, and because two processes are involved in connecting the components, i.e., a process of brazing the circuit board and the insulating board to each other and a process of joining the joined assembly to a base, the manufacturing cost of the heat spreader module is high.
The inventors of the present invention have disclosed in Japanese Laid-Open Patent Publication No. 2002-43482 a process of joining a circuit board, an insulating board, an intermediate layer, and a heat sink using a hard solder material while the components are heated under pressure. According to the disclosed process, the components are joined in one step, without leaving a joined layer that would pose a large heat transfer resistance. The disclosed process makes it possible to produce an inexpensive heat spreader module, which exhibits high thermal conductivity.
The inventors have also proposed a process of manufacturing a heat spreader module having a required bonding strength and without producing excessive hard solder material, together with a heat spreader module manufactured in this manner. For details, see Japanese Laid-Open Patent Publication No. 2004-303818, for example.
If the heat spreader connected to the heat sink is made of CuMo or the like, then the heat spreader needs to be formed into a wide shape in order to spread heat from the semiconductor device over a wide area. If multiple semiconductor devices are mounted on such a wide heat spreader, it is necessary for the semiconductor devices to be installed at spaced intervals. The circuit board, the insulating board, and the metal plate are interposed between the heat spreader and each of the semiconductor devices.
Conventional heat spreader modules are large in size, and the heat spreaders used therein are required to be large in thickness. Consequently, there have been limitations on efforts to reduce the weight, height, size, and cost of such heat spreader modules.